The present invention relates to an anticorrosion paint which employs polyaniline as an anticorrosion pigment, so as to prevent the corrosion of metal materials, in particular, of steel materials. More specifically, the present invention relates to an anticorrosion paint, which can provide persistently excellent anticorrosion effect without using metal which causes environmental pollution.
As generally known in the art, the corrosion of metal materials including steel is a serious problem in various industrial fields. The corrosion of steel brings enormous loss in property and industry, and half of steel production is consumed in replacing the corroded steel structures every year. Various anticorrosion paints have been used to prevent the corrosion of metal materials, especially steel materials.
The above-mentioned anticorrosion paint is composed of metal, which is utilized as general anticorrosion pigment, and organic polymeric resins/inorganic resin which makes the metal to adhere to the surface of steel and protects coated object from corrosive environments. The anodizing forming type using Pb, Cr and the like, and the sacrificial anode anticorrosive type using Zn have been previously used as anticorrosion pigments.
However, the anodizing forming type anticorrosion pigments are classified as heavy metal, and so have the defect of causing another environmental problem at the time of elution, and the sacrificial anode anticorrosive type anticorrosion pigments exert an anticorrosion capability with an electrochemical sacrificial mode using the ionization tendency of the anticorrosion pigment, so have a defect of being unable to protect metal materials from corrosion for long period of time because the capability of the sacrificial anode anticorrosion decreases as the corrosion of sacrificial metals increases over time.
Since the rust of metal materials results from the action of air, water or carbon dioxide, the anticorrosion paints should perform two actions: to prevent them from contacting the surface of metal materials and block chemically the generation of the rust. A paint for primer coat should have particularly strong adherence to a metal basis and a paint for top coat should not permeate any air or water through the coating of paint, the low occurrence of cracking, high durability and high weatherability.
The oil based paints, which contain the mixed drying oil and the anticorrosion pigment, and the red lead paints, which contain the mixed red lead (Pb3O4) and boiled oil, are mainly used as anticorrosion paints. The anticorrosion paints that can substitute for the red lead paints comprise zinc powder, lead suboxide, basic zinc chromate (zinc yellow), or basic lead chromate (zinc chromide) pigments, in which the latter two pigments have a chemical anticorrosion effect. Besides, the anticorrosion paints may contain iron oxide, Bengala alone, or zinc yellow and red lead as combination pigments. As vehicles, those suitable for the primer coat or topcoat paints are used, and oil varnish and synthetic resin varnish as well as boiled oil are usually used. Recently, the paint, in which basic zinc chromate, phosphoric acid and butyral resin are dispersed into a mixed solvent of alcohol, ketone and water, is used for anticorrosive treatment of metal materials including aluminum, zinc or tin.
However, the prior anticorrosion paints as described above have problems such as the environmental pollution or low persistence of the anticorrosion effect.
Meanwhile, polyaniline is known as a material hard to handle because it is insoluble and difficult to be dispersed, despite its excellent function, it has many limits in its application. A recent technical development is capable of dispersing polyaniline into a matrix resin and permits its application in various fields and the development of products using it, but any application to the anticorrosion paints has not been reported.
Accordingly, the present invention is made to solve the problems of the prior art and the object of the invention is to provide anticorrosion paints for steel using polyaniline which has an excellent anticorrosion effect, long persistence of the anticorrosion effect, high durability and superior coating property controlling the anticorrosion effect, without using metals which cause environmental pollution as an anticorrosion pigment.
Another object of the present invention is to provide a method of simply preparing the anticorrosion paint.
To accomplish the above objects and other objects which can easily follow upon the above objects, the present invention provides a coated steel substrate comprising an anticorrosion paint system, wherein the paint system comprise a primer coat paint layer and a top coat paint layer: a primer coat paint layer including 3 to 49 weight percent (wt %) of the polyaniline, 40 to 86 wt % of the matrix resin, 1 to 47 wt % of the additives and 10 to 56 wt % of the mixed solvent; and a top coat paint layer for protecting for protecting the primer coat paint layer and improving the anticorrosion effect, the top coat paint layer including 40 to 89 wt % of matrix resin, 5 to 54 wt % of colored pigment, 1 to 50 wt % of additives and 5 to 54 wt % of mixed solvent.
Also, the anticorrosion paint of the present invention is characterized in that it uses no metal which has mainly been used in the prior arts as an anticorrosion pigment to solve the defects of the previous anticorrosion paint, and it uses polyaniline with an excellent anticorrosion function as the anticorrosion pigment to provide excellent anticorrosion effect on metal materials, particularly steel materials.
The present invention will hereinafter be described in further detail regarding the anticorrosion paint for steel using the polyaniline according to the preferred embodiments of the present invention.
Generally, the polyaniline is classified into a fully oxidized type, a partially oxidized type and a reduced type depending on an oxidation degree. Although the emeraldine base form of polyaniline (PANI-EB) is in an insulated state, it is transferred to the emeraldine salt form of polyaniline (PANI-ES) in a conductive state by doping the PANI-EB in protonic acid, such as hydrochloric acid. Electric conductivity is changed by doping level, the used organic solvent, and the kind of dopant or molecular weight. By improving doping level, the insulator-metal transition phenomenon occurs. The PANI-ES plays a role as a charge carrier by the formation of polaron that has a mobile defect in one-dimensional chain structure.
Emeraldine salt (electric conductivity: xcx9c5 S/cm) is synthesized in powder form by oxidatively polymerizing aniline monomer using oxidants, such as ammonium peroxydisulfate(APS; (NH4)S2O8) in protonic acid solution including 1M hydrochloric acid(HCl). The emeraldine salt is transferred to the insulating emeraldine base (electric conductivity: xcx9c10xe2x88x9210 S/cm) by deprotonation in basic solution, such as ammonium hydroxide(NH4OH).
Since both forms of polyaniline (base and salt thereof) were not dissolved in solvent, they have been difficult to be fabricated, but after it was reported in 1986 that N-methyl-2-pyrrollidinone could be used as solvent, the polyanilines became to be fabricated into film, fiber or elastomer. When the film or fiber was stretched four times and then doped with 1M HCl, it represented an electrical conductivity of 220 S/cm. The degree of cross-linking is controlled by varying the molecular weight of the polyaniline used for fabrication of the film, the use of solution or the evaporation rate of the solvent, and the resultant diverse films represent various results in crystallinity, electric conductivity after doping, an electric conductivity mechanism and electromagnetic interference shielding capability.
Recently, since the polyaniline doped with the functional acid like camphorsulfonic acid or dodecylbenzenesulfonic acid is known to have an increased solubility in nonpolar or mild polar solvents, such as m-crezol or chloroform, film or fiber can be fabricated directly from the polyaniline doped with the functional acid in the conductive state. This resultant film showed the phenomenon of an electrical conductivity of 400 S/cm at its maximum, depending on solvent. This phenomenon has been described by the notion of xe2x80x9ceffectively doped sitexe2x80x9d formed in the chain of polymer, depending on solvent. Unlike the previous doped polyaniline film, it was confirmed that this resultant film has a high negative dielectric constant and exhibits the metallic electrical conductivity because the electrical conductivity of this resultant film is little temperature-dependent.
The polyaniline used as an anticorrosion pigment in the present invention is both emeraldine salt of a reduced type and emeraldine base of an oxidized type.
The polyaniline used in the present invention is prepared as follows (in which aniline monomer is purified before use, and ammonium peroxydisulfate, H2SO4 and formic acid are used as such):
(1) A solution of aniline (40 Ml) in 80:20 (v/v %) of 1M H2SO4 and formic acid (800 Ml) in a vessel 1 is first cooled to 0xc2x0 C. and a solution of ammonium peroxydisulfate (23 g) as an oxidant in 1M H2SO4 (200 Ml) in a vessel 2 is cooled to 0xc2x0 C. After the solution containing the oxidant of the vessel 2 is added to the solution containing aniline of the vessel 1 over 2 min while stirring with a magnetic bar, the resultant mixture is reacted for approximately 90 min while stirring with a magnetic bar. After that, the reaction mixture is filtered through a filter paper.
(2) The resulting filtrate from process (1) is added without aniline at 0xc2x0 C. to a solution of ammonium peroxydisulfate (23 g) in 80:20 (v/v %) of 1M H2SO4 and formic acid and then the solution reaches 1L of total volume. The resultant mixture is reacted for approximately 90 min, and then the reaction mixture is filtered through a filter paper three times.
(3) The resultant filtered solid from processes 1 and 2 is added again to 1M HCl solution, stirred to make a suspension, and then further stirred by a magnetic bar for approximately 15 min, and filtered through a filter paper to obtain the reduced form of polyaniline.
After the filtrate is washed with 1M HCl until it is completely colorless, the protonated polyaniline is obtained.
Such a preparation of polyaniline according to the present invention is characterized in that the process of adding the only oxidant without additional aniline to the filtrate obtained after synthesis is repeated three to five times and nearly similar polyaniline in the physiochemical properties such as an electrical conductivity and thermal stability is obtained.
Therefore, the synthesis of the present invention provides much higher yield than that of the prior art.
And the reduced form of polyaniline obtained from the above synthesis may be dedoped with 0.1M NH4OH to produce the oxidized form of polyaniline.
The molecular structure of polyaniline of the present invention is as follows: 
From the preparation of the present invention, the aniline monomer was synthesized to the polymerized polyaniline having 10,000 to 50,000 of molecular weight.
The content of polyaniline used in the present invention is preferably in a range of 3 to 49% by weight. When the content of polyaniline is less than 3% by weight, it results in the problems such as poor anticorrosion effect and a reduced persistence of anticorrosion effect. When the content of the polyaniline exceeds 49% by weight, the addition of polyaniline has little improvement so that it is not economical, and the film shows a tendency of being easily separated decrease of film durability.
First of all, the method of preparing a primer coat using polyaniline (either reduced form or oxidized form) comprises the step of mixing polyaniline, a matrix resin, various additives and mixed solvents at a predetermined ratio, and milling the mixture. The primer coat may further comprise an extender.
More particularly, 3 to 49% by weight (wt %) of polyaniline, 40 to 86 wt % of a matrix resin, 1 to 47 wt % of additives, and 10 to 56 wt % of mixed solvents are mixed, and the mixture is milled for 90 min using an attrition mill. If desired, an extender may be added to the mixture and the content of the extender is preferably in a range of 5 to 15 wt %. When the extender is added, the content of the matrix resin and the mixed solvents together should be decreased by the same amount as that of the extender.
The matrix resins are for example cellulose acetate propionate (100% of solid content), a thermoplastic polyurethane resin (50% of solid content), acrylic urethane (50% of solid content), epoxy ester (60% of solid content) or epoxy resin (100% of solid content), which can be used either alone or as a mixture of two or more.
The content of matrix resins is preferably in a range of 40 to 86 wt %. Where the resin content is less than 40 wt %, it is disadvantageous in that adhesion between the surface of metal materials and paint is decreased. Where the resin content exceeds 86 wt %, it is disadvantageous in that the content of polyaniline is relatively decreased and the anticorrosion effect is reduced.
As additives, a wetting dispersion agent, an anti-settling agent, a defoamer, an anti-cratering agent, an anti-sagging agent, a leveling agent, an anti-pinhole agent, or a plasticizer may be employed. It is preferred that a mixture of at least two kinds of the above additives are used according to the properties of the paint. The kind and content of the additives will be readily understood by those who skilled in the art.
The content of the additives should do not exceed total 47 wt %. Where the content exceeds 47 wt %, it is disadvantageous in that the adhesion between the surface of metal materials and the paint is greatly decreased.
As extenders, talc, calcium carbonate, barium sulfate or clay may be used.
As solvents, xylene, toluene, methyl isobutyl ketone, butyl acetate, ethyl acetate, cellosolve acetate, ethyl cellosolve, n-butanol, iso-butanol, isopropylalcohol, methyl ethyl ketone, cyclohexanone, methanol or diacetone alcohol may be used either alone or as a mixture of two or more thereof.
The top coat that is used to protect an anticorrosion paint for the primer coat and to improve an anticorrosion effect is prepared by adding 40 to 89 wt % of matrix resins, 5 to 54 wt % of colored pigments, 1 to 50 wt % of additives and 5 to 54 wt % of mixed solvents.
Epoxy resin or acrylic urethane resin may be employed as the resins, and inorganic or organic pigments, such as titanium oxide, iron oxide (reddish brown, yellow or black), phthalocyanine blue or phthalocyanine green, may be used after being mixed depending on a desired color, as the colored pigments. As the additives, a wetting dispersion agent, an anti-settling agent, a defoamer, an anti-cratering agent, an anti-sagging agent, a leveling agent, anti-decolorizing agent or an anti-pinhole agent may be employed.
As Solvents, xylene, toluene, methyl isobutyl ketone, butyl acetate, ethyl acetate, cellosolve acetate, ethyl cellosolve, n-butanol, isobutanol, isopropylalcohol, methyl ethyl ketone, cyclohexanone, methanol or diacetone alcohol may be used either alone or as a mixture of two or more thereof.
The present invention will hereinafter be described in further detail by examples and comparison examples. It should however be borne in mind that the present invention is not limited to or by the examples.